The milisecond in between saying/doing something very inapporopriate/embarassing/stupid/racist/sexist/etc and actually realizing what you just said and that fucked up real bad. This milisecond is usually followed by a silence, awkward staring, and you; feeling as though you'd want to just dissapear right away.

-you, telling an mean black joke
-insert the oh-fuck milisecond here
-realizing just a moment too late that your one black friend is there